I have a fuel problem that I would like your advice on. I have an RV-12 with the Rotax 912ULS that only has about 75 hours on it over the last three or four years. I had some severe medical problems and my RV also had some fuel problems. The fuel problems began with leakage from the tank. I built the tank as per Van's manual and it sat for about a year before I put any fuel into it. It was then OK for well over two years before there was a leak. It began as a minor leakage and I removed the tank and sealed, from the outside, one seam and a front corner. That did not stop the leak and it got worse to the point that the tank lost about three gallons of auto fuel over about four days. I removed the tank and could not find any sign of a leak with the tank on the bench even with fuel in the tank. I put the tank back in and filled it, again with auto fuel. It was OK for about five days and then began to leak again, this time it lost about ~five gallons and stripped the paint off the bottom of the plane, a real mess. I took a sheet of newspaper and slid it under the tank, before I removed the fuel, and found that it was leaking at the rear right corner. When I took the tank out that time it did not leak on the bench until it had sat there for over a week. The Pro-Seal softened up in places when it was wet with fuel but it was OK when it dried out. While it was wet I could poke a Q-tip stick through the corner, the Pro-Seal was quite soft. had no ideas why the Pro-Seal broke down as it did but rather than risk another leak in flight I made a new tank, this time without the side gauge and with a Moler mechanical gauge on the top. There was a lot of trouble starting the engine and when it did start, with full choke and no throttle, it ran rough. I had to run the engine on full choke for at least five minutes before I could even crack the throttle open. I cleaned both carbs and tried again. Before the five minutes were up if I tried to open the throttle the engine would die. Once it had really warmed up it seemed OK. I did the pre-flight check with a run up at 4000 rpm. The ignition drop as less than 250 rpm and both ignitions were the same. At full throttle I could not get more than 4400 rpm and it ran rough again. Back at the hangar I tried a few diagnostic things. With the electric fuel pump on I see about 2.5-2.9 psi. With the engine running and the electric pump off the fuel pressure drops to~0.5 psi. I took the fuel pump off the engine and operated it by hand, it seems OK but needs the electric pump on to keep it primed. The throw of the pump plunger is ~3/8"-7/16". Checking the pump cam with a rod and measuring the amount of difference from high cam to low cam it is barely 3/16" which seems very little. There is no sign of wear on the cam when looking at it through the pump mounting hole. I had thought that the pump filter was contaminated but the pump, when off the engine, seems OK.
The questions:
1) Is this a normal throw for this cam?
2) Why does it need so much choke when it did not do so before all the fuel problems.
3) Is there something else I am missing that would cause these symptoms?
Since pulling off the fuel pump off another mechanic remarked that the engine seemed very stiff to pull over with the prop, it had always been that way since new and I had attributed it to the engine gearbox combination. I removed the top plugs and the gearbox and the engine and the gearbox are each quite smooth but not when the gearbox is mounted back on the engine. It feels like the plugs are still in and there is compression pressure causing resistance?
I apologize for the long description.
Henry

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Henry:
I have been working with gas tank sealants for over 20 years. I do not know what form of PRO SEAL you used, what type did you use, the 890 or the 1440? But, I can tell you that ALL the gas tank sealants available in the USA will NOT work with AutoGas (MoGas) that contains ethanol. The gas will soften and cause leaks to the sealant. They are good, not great, with MoGas that does NOT contain ethanol. YET! The 'Aromatics' in gas will also attack tank sealants. Just not as fast as ethanol!
Also - Many, Many people put one layer of tank sealant over the top of the old sealant... Ya CAN'T do that! The sealants DO NOT stick to them selves once cured and especially after gas has been in the tank. You MUST remove all the old sealant - Get down to bare metal - And start again.
As for your rotax running rough.. Don't know... Maybe a broken part of the sealant has blocked some orifice. I would fix one problem at a time. Gas tank sure sounds like it should be first.
Barry
On Fri, Sep 1, 2017 at 10:37 AM, Henry Roden <krazydoc33(at)gmail.com (krazydoc33(at)gmail.com)> wrote:

Quote:

I have a fuel problem that I would like your advice on. I have an RV-12 with the Rotax 912ULS that only has about 75 hours on it over the last three or four years. I had some severe medical problems and my RV also had some fuel problems. The fuel problems began with leakage from the tank. I built the tank as per Van's manual and it sat for about a year before I put any fuel into it. It was then OK for well over two years before there was a leak. It began as a minor leakage and I removed the tank and sealed, from the outside, one seam and a front corner. That did not stop the leak and it got worse to the point that the tank lost about three gallons of auto fuel over about four days. I removed the tank and could not find any sign of a leak with the tank on the bench even with fuel in the tank. I put the tank back in and filled it, again with auto fuel. It was OK for about five days and then began to leak again, this time it lost about ~five gallons and stripped the paint off the bottom of the plane, a real mess. I took a sheet of newspaper and slid it under the tank, before I removed the fuel, and found that it was leaking at the rear right corner. When I took the tank out that time it did not leak on the bench until it had sat there for over a week. The Pro-Seal softened up in places when it was wet with fuel but it was OK when it dried out. While it was wet I could poke a Q-tip stick through the corner, the Pro-Seal was quite soft. had no ideas why the Pro-Seal broke down as it did but rather than risk another leak in flight I made a new tank, this time without the side gauge and with a Moler mechanical gauge on the top. There was a lot of trouble starting the engine and when it did start, with full choke and no throttle, it ran rough. I had to run the engine on full choke for at least five minutes before I could even crack the throttle open. I cleaned both carbs and tried again. Before the five minutes were up if I tried to open the throttle the engine would die. Once it had really warmed up it seemed OK. I did the pre-flight check with a run up at 4000 rpm. The ignition drop as less than 250 rpm and both ignitions were the same. At full throttle I could not get more than 4400 rpm and it ran rough again. Back at the hangar I tried a few diagnostic things. With the electric fuel pump on I see about 2.5-2.9 psi. With the engine running and the electric pump off the fuel pressure drops to~0.5 psi. I took the fuel pump off the engine and operated it by hand, it seems OK but needs the electric pump on to keep it primed. The throw of the pump plunger is ~3/8"-7/16". Checking the pump cam with a rod and measuring the amount of difference from high cam to low cam it is barely 3/16" which seems very little. There is no sign of wear on the cam when looking at it through the pump mounting hole. I had thought that the pump filter was contaminated but the pump, when off the engine, seems OK.
The questions:
1) Is this a normal throw for this cam?
2) Why does it need so much choke when it did not do so before all the fuel problems.
3) Is there something else I am missing that would cause these symptoms?
Since pulling off the fuel pump off another mechanic remarked that the engine seemed very stiff to pull over with the prop, it had always been that way since new and I had attributed it to the engine gearbox combination. I removed the top plugs and the gearbox and the engine and the gearbox are each quite smooth but not when the gearbox is mounted back on the engine. It feels like the plugs are still in and there is compression pressure causing resistance?
I apologize for the long description.
Henry

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75 hours over three years means auto fuel sat in the tank unused for some long periods. From what I've heard auto fuel only has about a two week shelf life. I worked on a Kitfox that had sat for long periods with auto fuel in its tanks, and the fuel left deposits in the tanks which, when re-filled, would soften and migrate to the filters, plugging them. It took only minutes for the filters to become plugged enough to kill the engine. The challenge was that you couldn't see the deposits, but you could sure feel it when you tried to drive fuel through them. Your two symptoms of requiring choke to run and inability to attain full rpm indicate a fuel flow problem, as you've already guessed and proven. If your tanks have become "varnished", you'll have to clean them thoroughly. On the Kitfox we rigged a fuel pump and circulated fuel through the tanks continuously for two weeks, replacing the cycled fuel daily, until the varnish was eliminated enough for it to run continuously.

1) Is this a normal throw for this cam? 2) Why does it need so much choke when it did not do so before all the fuel problems.
3) Is there something else I am missing that would cause these symptoms?
Since pulling off the fuel pump off another mechanic remarked that the engine seemed very stiff to pull over with the prop, it had always been that way since new and I had attributed it to the engine gearbox combination. I removed the top plugs and the gearbox and the engine and the gearbox are each quite smooth but not when the gearbox is mounted back on the engine. It feels like the plugs are still in and there is compression pressure causing resistance?
I apologize for the long description.
Henry

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